This invention relates to a method of making self-locking nuts of the prevailing torque type, in which the locking characteristic is provided by thermoplastic material.
Sauer U.S. Pat. No. 2,450,694, granted Oct. 5, 1948, discloses a prevailing torque type self-locking nut (hereinafter sometimes "the Sauer nut") comprising a one-piece metallic nut body having a threaded bore portion, a first end of which is adapted to be entered by a mating externally threaded member. At a second end of the threaded bore portion is an annular recess or well formed in part by a circumferentially continuous annular flange portion extending axially away from the first end. The flange portion includes a cylindrical surface coaxial with and confronting the axis of the threaded bore portion. The Sauer nut also includes a pre-formed nylon collar mechanically held in the recess. The flange portion is crimped to engage the upper surface of the collar, thus to retain the same in the recess and prevent the same from turning relative to the body. The collar has an internal cylindrical surface confronting and coaxial with the thread axis and having a diameter which is somewhat less than the major thread diameter, so that continued rotation of the externally threaded member, after it traverses the threaded bore portion, will cause it to engage the cylindrical surface of the collar to impress a thread therein and achieve the desired self-locking effect, all is known fashion.
The pre-formed collar of the Sauer nut has a radial thickness which is quite large, thus imposing certain limitations on the overall dimensions of the nut, which limitations are in certain cases undesirable, as will be more fully explained hereinafter.
The Sauer nut has long been, and continues to be, preeminent among prevailing torque type self-locking nuts.
However, for many years it has been evident that it is highly desirable to develop a new self-locking nut which is capable of being manufactured at a significantly reduced cost relative to that of the Sauer nut but which is at least as good as the Sauer nut as to all significant performance criteria.
The present invention has culminated the search for such a new nut.
The nut of the present invention can be made at a substantial reduction in cost relative to the Sauer nut, and is at least as good as the Sauer nut as to all significant performance criteria.
In addition, as noted, the manufacture of the Sauer nut entails crimping of the flange portion after the collar has been placed in the recess. This has two disadvantages. One, there is a limit to the hardness and hence ultimate tensile strength of the Sauer nut, as any heat treatment to develop that strength must be accomplished before the collar is placed in the recess and hence before the crimping operation. Also, the nut body blank of the Sauer nut cannot be cold formed of high work hardenable material. Two, in the Sauer nut, the crimped flange portion overlies and extends axially beyond the collar, thus contributing to the overall height of the nut without contributing to its locking ability or strength.
The present invention avoids the crimping operation and in fact does not involve any metal working operation after the formation of the nut body. Hence, with the present invention, the nut body may be heat treated to any desirable hardness, and hence strength, thus making it possible to achieve a nut of improved strength-to-weight ratio with respect to the Sauer nut.
Thus, with the present invention, for a given thread size a smaller and lighter nut can be utilized, or a stronger nut can be utilized, all to the benefit of the end user.
By eliminating the crimping operation, the present invention also avoids the necessity for the crimped flange or more load bearing threads can be built into the nut body for the small overall nut height.
Rieke U.S. Pat. No. 3,316,338, granted Apr. 25, 1967, discloses a prevailing torque type self-locking nut (hereinafter sometimes "the Rieke nut") in which an internally threaded metallic nut body is provided with an annular recess located axially adjacent one end of the nut thread. An annular groove is pierced in the recess to provide a double undercut-like configuration. The radial nut surface adjacent the recess is knurled to provide better adherence of a locking element. A bolt having a thread and a smooth shank which corresponds to the core diameter of the nut thread is turned into threaded engagement with the nut thread, with the smooth shank in registry with the recess. This assembly is then dipped in plastic powder, so that the recess is filled with powder which is also mounded up along the bolt shank. Thereafter the bolt-nut assembly, with powder, is placed on a heating plate to carry out a fusing process by heating the same to the melting point of the powder which is thereby fused into a unitary body said to be firmly bonded to the nut body after cooling and solidification. After cooling, the bolt is unscrewed from the nut in the direction such that the shank traverses the nut thread. The cooled plastic material, which extends over the face of the nut body, is said to form a unit with the nut.
The nut body of the Rieke nut is complex and therefore expensive to manufacture, especially due to the necessity for piercing the double undercut groove in the recess. Also, it is noted that the radial dimension of the recess is quite large, resulting in a locking element which has a ratio of axial length to radial thickness, apparently not greater than about 1, which is on the same order of magnitude as the ratio of the axial length to radial thickness of the pre-formed collar of the Sauer nut.
With the disclosed method of making the Rieke nut, it is impossible to prevent the plastic locking element from extending over the adjacent face of the nut body. Furthermore, such method is not adaptable to mass production techniques.
Newnom U.S. Pat. No. 3,975,787, granted Aug. 24, 1976, discloses a prevailing torque type self-locking nut (hereinafter sometimes "the Newnom nut") having a standard metallic nut body having a circumferentially uninterrupted internal screw thread. The self-locking feature is derived from a ring-like plastic patch having a circumferential extent of greater than 180.degree. adhered to the thread of the nut body. The Newnom nut is satisfactory for applications which do not require the performance capabilities of the Sauer nut. The Newnom nut is made by a method which involves seating the nut body, either end first, on a pin a tapered portion of which cooperates with the circumferentially uninterrupted thread to define a cavity into which powder of the plastic material is inserted. The nut body is then heated to melt the powder.
It is therefore an important object of the present invention to provide a prevailing torque type self-locking nut which is of significantly lower cost than the Sauer nut but which is at least as good as the Sauer nut as to all significant performance criteria.
It is another object to provide a prevailing torque type self-locking nut having a nut body provided with a circumferentially uninterrupted internally threaded portion and a well portion surmounting the threaded portion and a locking element of thermoplastic material in the well portion and bonded to the wall thereof.
It is a further object to provide a prevailing torque type self-locking nut which is not subject to the dimensional limitations required of the Sauer nut or the Rieke nut.
It is an additional object to provide a method of making a prevailing torque type self-locking nut, which method is simple and inexpensive and at the same time reliable and readily adaptable to mass production techniques.
Additional objects are to provide a pin which is useful in carrying out the method and a nut body which is a component of the self-locking nut and which can be produced, as by cold forming, at reduced cost relative to the nut body of the Sauer nut.